Hi out there,

Have had my GS/3 (without paddle) for half a year now and I have a problem ... the shot volumes vary so much that it can't be right.
Grinder settings (Mahlkönig PRO M) and beans are totally unchanged. This morning I made an espresso which came out fine. Then at lunch time I made another and it came out approx. at double volume ...

It is current set with CRONO function off. Earlier (a month ago) it was ON, but I was annoyed by the varying volumes, so I tried setting it OFF. Worked for a while, but now it is totally crazy.

What is the matter?

Hmm espresso is basically water with some dissolved coffee solids so why not as a test just run it without coffee? That way you can see if the flowmeter is at least dispensing reasonably repeatable volumes.

Myself I never ever had an issue with wildly inaccurate volumes with the many machines I've owned with flowmeter dosing.

Also the GS/3 AV has a hard set 53 seconds maximum extraction, regardless if the desired volume is reached or not. To my knowledge this is unchangeable.

Are you sure the extraction is really varying? In order to determine this, you must measure the extraction by weight, not by volume. Volume is not an accurate measure of espresso extraction because the crema height is too variable.

Although your post doesn't say so, I'm going to assume, like the other poster, you're using the volumetric dosing buttons. Most of what I say below applies to volumetric dosing.

But regardless of whether or not you're using the volumetric buttons, bear in mind that the most common causes of shot variation is the grinder not producing a consistent grind. This requires a high-quality grinder with burrs in good condition, adjusted properly. What grinder are you using and what's the condition of the burrs?

Another common cause of shot variation is poor distribution technique. Some grinders or coffees require that you use the Weiss Distribution Techniques WDT (essentially stirring the grinds) or the RDT (can't remember what R stands for, but it means slightly wetting the beans before grinding.)

Now, if you're using the volumetric buttons:

My experience with GS/3 AV volumetric dosing is that it's not accurate enough for precisely repeating shots, but I've not seen it be "wildly" off. It's been many years since I tried using volumetric dosing, but my vague recollection is that sometimes it would repeat perfectly and sometimes it would be off by 10%-20% or so. I concluded it wasn't accurate enough to repeat optimum extraction.

I don't know why the GS/3 volumetric dosing isn't accurate. Others have said that the flow meter used in the GS/3 is a fairly inexpensive model and that to get precise flow measurement a more expensive flow meter would be required. I can't speak to the accuracy of other LM models, like the Linea, but I suspect that cafe baristas don't worry all that much about precisely repeating optimum extractions.

Unless you're trying to use the GS/3 in a cafe setting, I wouldn't bother with volumetric dosing. You should learn how to repeat shots manually. A big step in that direction is to use a scale to weigh the shot as it's extracting. You want the shot to blond at the same time that you hit the desired brew ratio, with the time being in the sweet spot for espresso, about 25-35 seconds (give or take.) With light roasts you'll need to extract longer. Once you nail down your distribution technique, you can use the shot timer to repeat shots during the same session (i.e, when it's not likely aging of the coffee will change the flow rate.)

Finally, in response to the other poster, the extraction timer on the stock GS/3 limits shots to 50 seconds (not 53 seconds). That can be extended to 55 seconds by programming one of the volumetric dosing buttons to do a 5 second preinfusion followed by a pause of minumum time (I think the minimum is 0.1 seconds, but I don't remember.) There's a version of the firmware that extends the timer to as much as 120 seconds, but you'd have to get it from the LM factory in Italy and you need some special equipment and technical expertise to load it.

I performed some measurements on the flow meter - and also according the the Gicar datasheet they are pretty darned accurate +-2% but repeatability should be 0.2%.



Flow rates:


This assumes the pressure on the inlet is constant. So pressure regulators upstream: Yay. Gear pumps upstream - no do. Flow restricting needle valves upstream - ditto - no do.

That said, if you run it w/PF empty - it should be withing 1% by weight. If it isn't - open the AV sensor up and clean the nozzle and vanes. Be careful about the connectors - they can break and it is expensive!

Dick is right that LM chose the wrong AV sensor - they chose the largest nozzle model for the AV sensor - which is good and bad - bad since sensitivity and accuracy are diminished. Good since it clogs less.

More about the sensor here:

Gicar flowmeter accuracy

LM actually uses gicleur downstream of the flowmeter. On the GS/3 this would be on the group tube for the brew solenoid. The nozzle diameter on the GIcar spec I think it is on the inlet of the flowmeter and I am not sure what the pressure drop for the flowmeter.
Have you measured the free flow rate of the machine? It should be around 500 ml/min.

Boostownjoo - I don't know if the comment was meant at my previous comment.

If it is - the nozzle I was referring to is the nozzle inside the flow meter that cause the vanes to rotate. It is a large nozzle for the flow rate.

As you stated - of course there is the Ruby gicleur (also a nozzle) downstream.